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Why Not Mirror In The Volume Manager?: Page 2 of 2

As I talk to users and vendors about their data protection schemes, I've noticed that many organizations protect their mission-critical applications by synchronously mirroring data from a primary array to a secondary array. They then replicate from the secondary array off-site, or off-campus, asynchronously to a third target. As I think about this architecture, I've started wondering if companies might not be better off mirroring to the primary and secondary arrays directly from their servers, r
Howard Marks
December 07, 2010

At the low end, some server-based array products support synchronous replication to make up for their single points of failure at the motherboard and/or disk controller. Unfortunately, I've seen that actually using this feature can have a significant negative impact on disk I/O performance. It may just be asking too much from a server motherboard to manage a bunch of storage and keep a doppelganger in sync at all times. Mirroring at the host could provide the single point of failure avoidance with a smaller performance impact.

Clearly, host replication isn't a replacement for synchronous replication. I wouldn't want to mirror a host to arrays in different data centers if there were any significant latency from the server to the more distant array. Even 100 microseconds of additional latency would make a mirrored pair of arrays feel more like a SATA and a SAS mirrored together with performance matching the slower of the pair.

Other than "it's just wrong," why don't more users mirror from the host? Comments, and reasons, welcome.

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